The purpose of this project is to determine the role of renal metabolism in support of segmental filtrate reabsorption in the mammalian nephron. To accomplish this, we are using renal micropuncture techniques to analyze the function of the single nephron in the in vivo rat kidney. Simultaneously, we are measuring whole kidney function and metabolism by clearance and extraction techniques. By comparing these data under physiological conditions specifically imposed upon the experimental preparation information can be obtained as to the role of renal metabolism in support of single nephron function. Our present project proposes to determine the interrelationships between renal oxygen consumption and segmental filtrate reabsorption in the isotonically volume expanded rat.